The present invention relates to a method and apparatus for providing backlight compensation and, more particularly, to a method and apparatus for backlight compensation for minimizing the interference of the surroundings of a monitoring camera and ambient illumination while photographing an object with the monitoring camera.
When photographing an object in a normal mode with a monitoring camera installed in a predetermined place with a surrounding illumination condition such as the sun, an incandescent light, or the headlights of cars at night, the object is placed in a backlight illumination state and thus a shaded and blurred image is obtained.
That is, when photographing the object without setting a backlight compensation mode, i.e. in a normal mode, the light intensity is controlled by closing down an iris in accordance with the luminance signal level of an illuminant, which is incident through the iris without any allowance for the luminance signal level of the object, thereby producing the shaded and blurred image of the object on a screen. To circumvent the problem, a monitoring camera has a backlight compensation (backlight compensation) function. The backlight compensation function serves to obtain a desired clarity by reducing the influence of the illumination on an object and any other interference for the purpose of ensuring a desired image quality of the object.
In a conventional backlight compensation apparatus, the user manually selects a backlight compensation area from among a predetermined number of backlight compensation areas (e.g. fire backlight compensation areas). The user manually selects the most appropriate backlight compensation area for the surroundings and an ambient illumination of the monitoring camera by operating one of a plurality of selecting keys, each with selecting key corresponding to a fixed backlight compensation area. Precise backlight compensation area selection is difficult since the selection appropriate for the various surroundings of a monitoring camera relies on a user's judgement.
Moreover, even when an appropriate selection of one backlight compensation area is made in connection with an ambient illumination, the backlight compensation area must be redesignated whenever the ambient illumination conditions change. Otherwise, the backlight compensation function of the monitoring camera may be lost or may not work satisfactorily.
Accordingly, in the convention backlight compensation function, it is inconvenient to redesignate backlight compensation areas whenever a object moves or illumination conditions or watch angles change. Furthermore, when photographing an object in an outdoor setting, the backlight compensation areas must be continually redesignated due to changes in the natural light caused by the passage of time. Failure to do so will result in a deterioration of the clarity of the photographed object.